In the art of well boring, a borehole is drilled into the earth through the oil or gas producing subterranean formation or, for some purposes, through a water bearing formation or a formation into which water or gas or other liquids that are to be injected.
Completion of a well may be carried out in a number of ways dependent upon the nature of the formation of interest. Where the formation itself or formations above the formation of interest have a tendency to disintegrate and/or cave into the hole, like e.g. sand formations, it is known to use a filter apparatus to control unconsolidated formation elements while allowing the passage of oil or gas from the formation in conjunction with particles or solids.
For example, in sand formations, one common type of filter apparatus, called gravel pack, involves placing a control screen in the wellbore and packing the annulus between the screen and the wellbore wall with control particles of a specific size designed to prevent the passage of formation sand. Such control particles are made of a granular material such as for example gravels, ceramics or sintered bauxite. The main objective is to stabilize the formation while causing minimal impairment to well productivity, which means that it is critical to completely pack the space between the screen and the formation, preventing the movement of formation particles.
In addition to the use of control screens or similar apparatus, gravel packing operations may involve the use of a wide variety of control equipment, including liners (e.g., slotted liners, perforated liners, etc.), combinations of liners and screens, and other suitable apparatus. A wide range of sizes and screen configurations are available to suit the characteristics of the control particles used. Similarly, a wide range of sizes of control particles are available to suit the characteristics of the unconsolidated formation elements. The resulting structure presents a barrier to migrating sand from the formation while still permitting fluid or gas flow.
Another type of filter apparatus involves placing a control screen in the wellbore and packing the annulus between said control screen and the wellbore wall with control particles of a specific size designed to keep formation fissures open. In this case, the control particles, called proppant agents, may be for example sand or stone, ceramics or sintered bauxite.
In any event, after a period of production, injection or transportation of fluids or gases, there is a tendency for the interstitial space between control particles to become plugged with various types of residues. For example, organic residues like paraffin, asphalts and other agglomerating residues of petroleum origin often cause plugging problems. Usually these deposits may cause significant problems, because of their composition and the fact that they may precipitate under certain conditions (pressure, temperature, liquid composition, injection . . . ).
These materials of mineral or organic origins either together with chemicals from water, normally produced with the oil, such as, calcium carbonate, calcium sulfate, barium sulfate, sulfur and the like, or such chemicals themselves have a tendency to form extremely hard deposits on different parts of the components. Such deposits may adhere to the control particles, blocking the interstitial spaces between said control particles, therefore reducing or completely preventing the flow of fluids or gases through the control particles to the borehole. Similar problems may also be encountered due to precipitates build on the control screen, due to pressure drop and temperature considerations and the gravel pack like e.g. solid salts (for example calcium or barium sulfates, calcium carbonate, calcium/barium scales, etc. . . . ).
Another challenge encountered while using a control apparatus is migrating fines that plug the control particles and the control screen, impeding fluid flow and causing production levels to drop. As used in this disclosure, the term “fines” refers to loose elements, such as formation fines, formation sand, clay particles, coal fines, resin particles, crushed control particles, and the like. These migrating fines may also obstruct fluid pathways through the control apparatus lining the well. In particular, in situ fines mobilized during production, or injection, may lodge themselves in control screens, preventing or reducing fluid flow there through. Migrating fines may also be associated with either organic and or mineral precipitation byproducts downhole.
Well-stimulation techniques using chemical agents, such as matrix acidizing, have been developed to remediate wells affected by these problems. An existing solution using chemical agents for cleaning gravel packs is described e.g. in patent U.S. Pat. No. 7,896,080B1. In matrix acidizing, thousands of gallons of acid are injected into the well to dissolve away precipitates, fines, or scale deposits on the inside of tubular parts, trapped in the openings of the control screen, or in the pore spaces of gravel pack or matrix formation. However, acidizing may not in all cases allow in most cases dissolving significant amounts of the plugging materials as acid does not penetrate more than a few inches behind the control screen. Moreover, chemicals may damage the control particles, which can break into pieces or in the case of clays swell them, therefore reducing or completely preventing the flow of fluids or gases through the control particles and the control screen. Furthermore, existing chemicals treatments may not be efficient in horizontal boreholes due to the volumes required or the paths the chemicals take. Additionally, the acid must is usually removed from the well. Often, depending on well fluids and reservoir composition, the well must also be flushed with pre- and post-acid solutions. Aside from the difficulties of determining the proper chemical composition for these fluids and pumping them down the well, the environmental costs of matrix acidizing can render the process undesirable. Additionally, matrix acidizing treatments generally only provide a temporary solution to these problems and do not take into consideration root cause.
Alternative mechanical techniques may also be used to clean gravel packs. For example, a cleanup liquid may be introduced into control particles utilizing pressure pulses or jets as described in patent application US2005061503A1 or in patent application US2007187090A1. Typically, these techniques do not facilitate removal of significant amounts of the plugging materials as the cleanup liquid does not penetrate more than a few inches behind or into the control screen. There are also instances where, the cleanup liquid may damage the control particles, which can break into pieces, therefore reducing or completely preventing the flow of fluids or gases through the control particles to the screen. Furthermore, such techniques are not efficient in horizontal borehole as the cleanup liquid falls down with gravity.
It is therefore an object of the present disclosure is to provide an improved method and device for efficiently, rapidly, easily and effectively cleaning control particles arranged in a borehole extending into the earth without damaging said control particles or degrading the nearby environment. Another and further object of the present invention is to provide an improved method and device for removing deposits encrusted on control particles, in particular in areas where the control particles are accessible with difficulty or inaccessible. Yet another object of the present invention is to provide an improved method and device for increasing the production of fluids or gases from a subsurface earth formation or increasing the injectivity of fluids or gases into such formations.